There are a variety of semiconductor lasers that emit an elliptical beam. For example, many GaAs-based lasers operating at wavelengths such as 650, 780, 810 and 850 nm all emit an elliptical beam. In particular, a conventional 980 nm InGaAs laser, often used as a pump laser source for optical amplification systems, emits such an elliptical beam. Since the associated optical systems utilize transmission fibers with a circular core, much of the launched power may be lost. In particular, conventional optical systems will capture only approximately 40% of the launched power from an elliptical beam.
One known solution to this problem is to utilize an anamorphic fiber micro-lens, which achieves a coupling efficiency of about 70%. However, the microlens requires very stringent alignment tolerances. Additionally, the ellipticity of the launched beam may vary, depending upon the manufacturer (for example, the ratio of far-field angles between the vertical and horizontal directions can vary from 2.5 to 4.5, depending upon the manufacturer). Thus, even the best anamorphic microlens design may not be suitable for all situations.
Therefore, a need remains in the art for a system of improving the coupling efficiency of elliptical beams into a single mode optical fiber.